Photocontrollers are typically mounted on street lights and operate to turn the light off during the day and on at night. Since the cost of servicing a single street light can cost $100 or more on busy roads and in busy areas, and since there are 60,000,000 street lights in the United States alone, the problem of servicing faulty photocontrollers is severe. For example, when the relay of the photocontroller fails, or when the photocell fails, the street light will remain on during periods of daylight thereby wasting electricity. Alternatively, a faulty relay or a faulty photocell could cause the lamp to remain off during the night causing a safety hazard. Since repair typically occurs during daylight hours, it is often difficult to detect the latter condition.
The problem of high pressure sodium (HPS) street lights cycling at the end of their useful life is also severe. The phenomena of cycling of HPS lamps as they age from use is caused by some of the electrode material being plated off the electrodes and then being deposited on the inside of the arc tube. This makes the tube darken and traps more heat inside the arc tube. As a result, an increased voltage is required to keep the lamp ignited or ionized. When the voltage limit of the ballast is reached, the lamp extinguishes by ceasing to ionize. Then, the lamp must cool down for several minutes before an attempt at re-ignition can be made. The result is “cycling” wherein the worn out lamp keeps trying to stay lighted. The voltage limit is reached, the lamp extinguishes, and then after an approximately one-two minute cool down period, the arc tube re-ignites and the light output increases again and until the voltage limit is reached whereupon the lamp again extinguishes.
Cycling may waste electricity, cause RFI (radio frequency interference) which adversely effects communication circuits, radios, and televisions in the area, and may adversely effect and prematurely wear out the ballast, starter, and photocontroller.
For example, if an HPS lamp undergoes cycling for a many nights before it is finally serviced and replaced, the ballast or starter can be damaged or degraded. But, when the HPS lamp is replaced, this damage or degradation might not be detected. Later service calls then must be made to service these problems. The ballast and starter components are more expensive than the lamp or the photocontroller.
The cycling problem is well documented but, so far, the only solutions offered are to replace the HPS lamps with less efficient mercury lamps or to reconfigure existing photocontrollers with a special fiber optic sensor which senses light from the lamp and sends a signal to a microprocessor to indicate whether the lamp is on or off. After three on/off cycles, the microprocessor turns the lamp off and turns on a red strobe light which can be seen from the street. Unfortunately, this prior art solution requires modifications to the existing light fixture (e.g. a hole must be drilled in the fixture housing) and the use of an expensive fiber optic sensor. See, e.g., U.S. Pat. Nos. 5,235,252 and 5,103,137 both incorporated herein by this reference.
Another problem with all luminaries including HPS or other types of lamps is the cost involved in correcting the cycling problem and other faults such as a lamp out condition. For example, a resident may report a lamp out or a cycling condition but when the repair personnel arrives several hours later, the lamp may have cycled back on. Considering the fact that the lamp pole may be 25-35 ft high, repair personnel can waste a considerable amount of time checking each lamp in the area. Also, repair and maintenance personnel may not be able to service a given residential area until daylight hours when all of the street lights are off by design.
In U.S. Pat. No. 6,028,396 (also incorporated herein by this reference), the photocontroller includes a microprocessor programmed to detect whether the lamp to which it is attached is faulty, i.e., either out or cycling. When the lamp is turned on, the load drawn by the lamp is read by the microprocessor at times t1 and t2 and the load difference is calculated. If the load difference is less than about 12.5%, the lamp is determined to be out because a properly working lamp consistently draws more and more of a load during a start-up condition while a failed lamp or ballast does not.
Furthermore, by continuing to read the loads at times t3- . . . tn and counting the number of times the load reading at any two readings is lower than about 25% provides an indication of a cycling event.
In co-pending applications Ser. No. 09/544,307, a faulty relay condition is detected when the lamp draws a load even when it is off. A faulty photocell condition is detected when the lamp continuously draws a load (and is thus on) even when it is daytime.
In each case, the microprocessor outputs a fault detection signal and causes one or more indication events to occur. The photocontroller so programed has performed well and has been well received in the industry. Different customers, however, desire different ways of providing an indication of when a fault event is detected.
For example, some customers, when a cycling fault is detected, want the light turned off immediately and an LED resident on the photocontroller to flash. Accordingly, this option is programmed into the microprocessor as “option A.”
Different customers, when a cycling event is detected, want the light to remain on even in the daytime so it can be readily seen by repairmen. This “cycling day burner” option is programmed as “option B.”
Still other customers, when a cycling fault is detected, ask that the light be turned off and kept off always thereafter. This is programming “option C.”
One interesting concern that has occurred when different photocontrollers were programmed according to these different options is that quality assurance inspectors have a difficult time insuring at the factory that the correct programming option is resident in the photocontrollers. Still another interesting problem uncovered by the inventors hereof was that a fault signal was only provided when there was a fault, i.e., there was no way to quickly and positively ascertain whether the photocontrol was operating properly since there was no positive indication when the photocontrol during testing performed correctly. Moreover, it takes some time for the transients to settle and the lamp to warm up during factory testing adding to the cost of and the time consumed by final product testing.